Citation

In 2008, Deltares wrote a report called “Development of a framework for Appropriate Assessments or English offshore windfarms” (Prins et al. 2008) as a basis or guideline for the Appropriate Assessments for nineteen initiatives for offshore windfarms (OWFs) on the Dutch continental shelf (DCS). This report is further referred to as the "Framework".

This Framework gave an overall description of the possible negative ecological effects of the construction and operation of OWFs on natural values protected by the European Bird and Habitat Directives and gave guidelines for the quantitative methods for estimating these effects in the project-specific Appropriate Assessments (AAs).

Within the legal context of the European Bird and Habitat Directives (BHD), and based on the Framework, the project-specific Appropriate Assessments zoomed in on three major ecological effects of OWFs, namely:

Possible collisions of birds, both from breeding colonies and during the migration seasons during the operational period of the OWFs.

Mortality of fish larvae by underwater sound during piling of the OWF monopile foundations and the effects of reduced fish densities on the food availability for birds and marine mammals.

Loss of habitat (quality and quantity) of marine mammals due to underwater sound during piling of the OWF foundations and during their operational period.

After completion of the AAs, a process was started to fill the knowledge gaps about the possible negative environmental effects of the construction and operation of OWFs. The first part of this was the establishment of an overarching plan for researching the ecological effects of offshore windfarms. This so-called Masterplan (MP) described the whole of the cause-effect relationships, a comparison with existing knowledge, and the derivation and ranking of research ideas and concrete proposals (Boon et al. 2010). These proposals were then further prioritized, after which funding was found for a first series of research. The first series of research proposals ("shortlist") has been carried out in 2010 and 2011, and is currently completed. The results of this shortlist research have been published in separate reports.

The shortlist research, and the research that is carried out in recent years in the two already existing offshore windfarms Offshore Windpark Egmond aan Zee (OWEZ) and Prinses Amalia Windpark (PAWP), has increased the knowledge with regard to ecological effects substantially. The increase in knowledge and the next steps needed to further this knowledge have been described in a separate document (Boon 2012).

To facilitate the use of this updated knowledge, Rijkswaterstaat asked Deltares for a description of the implications of the results from the aforementioned investigations on:

The restrictive conditions for the constructions of OWFs as have been described in the permits for OWFs.

The spatial planning of OWFs.

Preventing and mitigating the negative ecological effects of the construction, and operation of OWFs can be subdivided into the following aspects:

Temporal considerations: what is the best period in the year for the construction of OWFs? Also, during the operation of OWFs, temporal measures can be considered: shutting down the OWF during periods of migrating birds passing by the OWF.

What are the technical possibilities that, apart from the spatial and temporal planning aspects, may contribute to mitigating any negative environmental effect?

Spatial considerations: what is the best location for planning OWFs with respect to possible environmental effects on marine life? This is treated in chapter 4.

Technically, the first two aspects fall under “prevention”, and only the last aspect is “mitigation”. Mitigation is the term that covers all measures that can be applied to reduce negative environmental effects during the construction or presence of OWFs. At the moment, the licenses restrict the construction of OWFs to the second half of a year; this prevents the occurrence of significant negative effects of piling on marine organisms.

It should be mentioned that the results of the “shortlist” program contribute to the first two aspects only: prevention of environmental effects by planning the construction in time, and by choosing the locations that affect marine life in the least. Construction interacts with both the spatial and temporal aspects; there might be locations and time periods that give less negative effects on marine life. The operational phase relates to the spatial aspect; once the OWF is in place, there is no temporal component to preventing the ecological impacts, apart from shutting down the OWF, although strictly this should be seen as a mitigative measure and not a preventive measure. Technical measures apply on all phases of construction and operation, and may broaden the window in time and space for the planning of these phases.

This report will not treat the technical measures of mitigating the negative ecological effects of the construction and operation of OWFs. Such technical measures, such as changing the configuration of OWFs (affecting bird impact), using under water screens for dampening underwater sounds due to piling, different piling techniques (affecting mammal and fish impact), etc. have been and are subject of some studies (see e.g. Nedwell & Howell 2004, Nehls et al . 2007, Drewitt & Langston 2008). There is even a UNESCO initiative (The International Quiet Ocean Experiment), which started last year. However, until now, results on the effects of these technical measures are inconclusive. Therefore, no advice can be given on generic and effective technical measures that mitigate the negative ecological effects of construction and operation of OWFs.

Below, the possibilities for prevention are discussed, subdivided by the cause-effect relationships per planning phase. It should be stressed that this report only gives a first overview of what possible implications exist for the prevention of ecological effects in policy and licensing based on the recent advancements of ecological cause-effect relationships. A next step would involve a more detailed study on both temporal and spatial aspects of preventing ecological effects of the construction and operation of OWFs. However, to set up such a follow up, additional data and choices are required, which involves a more in-depth discussion with policy makers and researchers. This was not possible within the time frame of this study, Moreover, the effectiveness of doing such a study will be improved by integrating the results of this study with the results from the shortlist studies and the possibilities for the next research round (Boon 2012) and with the currently ongoing study on the methodological update of the Framework (Boon et al. 2012).